THE PERCEPTION OF SPACE. 137 



"We must distinguish roomy from superficial, as well as distinctly 

 from indistinctly bounded, sensations. The dark which with closed eyes 

 one sees before one is, for example, a roomy sensation. We do not see 

 a black surface like a wall in front of us, but a space filled with dark- 

 ness, and even when we succeed in seeing this darkness as terminated 

 by a black wall there still remains in front of this wall the dark space. 

 The same thing happens when we find ourselves with open eyes in an 

 absolutely dark room. This sensation of darkness is also vaguely 

 bounded. An example of a distinctly bounded roomy sensation is that 

 of a clear and colored fluid seen in a glass ; the yellow of the wine is 

 seen not only on the bounding surface of the glass ; the yellow sensa- 

 tion fills the whole interior of the glass. By day the so-called empty 

 space between us and objects seen appears very different from what it 

 is by night. The increasing darkness settles not only upon the things 

 but also hetiveen us and the things, so as at last to cover them com- 

 pletely and fill the space alone. If I look into a dark box I find \t filled 

 with darkness, and this is seen not merely as the dark-colored sides or 

 walls of the box. A shady corner in an otherwise well-lighted room is 

 full of a darkness which is not only on the walls and floor but between 

 them in the space they include. Every sensation is there where I ex- 

 perience it, and if I have it at once at every point of a certain roomy 

 space, it is then a voluminous sensation. A cube of transparent green 

 glass gives us a spatial sensation ; an opaque cube painted green, on 

 the contrary, only sensations of surface." * 



There are certain quasi-motor sensations in the head wlien 

 we change the direction of the attention, which equally seem 

 to involve three dimensions. If with closed eyes we think 

 of the top of the house and then of the cellar, of the distance 

 in front of us and then of that behind us, of space far to the 

 right and then far to the left, we have something far stronger 

 than an idea, — an actual feeling, namely, as if something in 

 the head moved into another direction. Fechner was, I 

 believe, the first to publish any remarks on these feelings. 

 He wa-itcs as follows : 



" When we transfer the attention from objects of one sense to those 

 of another we have an indescribable feeling (though at the same time 

 one perfectly determinate and reproducible at pleasure) of altered direc- 

 tion, or differently localized tension {Spannung). We feel a strain for- 

 ward in the eyes, one directed sideways in the ears, increasing with 

 the degree of our attention, and changing according as we look at an 

 object carefully, or listen to something attentively ; wherefore we speak 

 of straining the attention. The difference is most plainly felt when 



* Loc. cit. S. 572. 



